Production of clear transparent polymers



Patented June 9, 1953 PRODUCTION (I) F CLEAR, TRANSPARENT OLYMERS Robert F. Leary, Cranford, N. J., assignor to Standard Oil Development Company, a corporation of Delaware N Drawing. Application December 31, 1949,

Serial N0. 136,392

1 Claim.

This invention relates to the production of valuable copolymers which are transparent when sheeted.

For many specialty purposes, it is desirable to prepare clear transparent sheets of polymeric material. This is fairly simple to do when polymerizing a single monomer but in many cases it is very difficult to obtain clear product when copolymerizing two or more monomers, as in copolymerizing styrene and isobutylene at low temperatures, e. g. C. to .-l03 C., by a Friedel- Crafts catalyst, as disclosed in U. S. Patent 227M749. In general, outside of impurities, it has been found that this lack of clarity or cloudiness is due to two factors: the heterogeneity of the polymer with respect to composition and molecular weight and the residual catalyst remaining in the final product. Satisfactory methods are known for removing virtually all of the residual catalyst from the polymer but difficulty has been obtained in overcoming heterogeneity due to composition and molecular weight. It has been established that the compositional heterogeneity is largely due to the fact that the compounds being copolymerized have difiere'ntsp'eeds of polymerization. For example, when a feed batch containing equal weights of styrene and isobutylene was polymerized with aluminumchloride catalyst, it was found that the first product that formed contained less than 35% by weight of styrene and the product obtained near the end of the reaction contained about-97% by weight of styrene.

Furthermore, the properties of a, copolymer depend partly upon the ratio of the monomers in the final product. Thus, copolymers of isobutylene and styrene range from viscous liquids to hard resins, depending upon the ratio of the monomers in the copolymer and upon the molecular weight. For a given purpose,.therefore, it is extremely desirable to be able to prepare a product containing a predetermined homogeneous ratio of monomers. Up to now this has not been possible when copolymerizing monomers which have different rates of copolymerization.

It has been proposed in U. S. Patent No. 2,100,900 issued November 30, 1937, to H. Fikentscher and J. Hengstenberg'th-at' substantially uniform products can be obtained by adding the compound'having the higher speed of polymerization at about the rate a-t'which itis used up. However, this method of obtaining an apparently uniform product does not guarantee that the product at any given time is a copolymer of the monomers in the specific ratio indicated. Instead the results mustbaan ayerage tast -88.1)

value of a number of copolymers having difierent ratios of monomers. Also, this method of operation does not teach those skilled. in the art how to produce a uniform product of a desired mono- I'nric ratio. For example, it has been found that if the weight ratio of styrene to isobutylne is iintially' about 2:1 then the first product formed contains 50%; by weight of styrene and 50% by weight of isobutylene. Therefore, in order to consistently obtain a product of this ratio, the weight ratio of the monomers in the polymerization mixture would have to be maintained constant,- L e. at 2:1, but this is difficult to do.

The-above disadvantages ofthe prior methods are overcome and a substantially homogeneous clear ransp c polymer is obtained from a mixture of monomers having different speeds of polymerization by first separately introducing catalyst and feed; which: may contain a diluent as well as comonomers in a definite ratio, into a reaction vessel until desired equilibrium mixture is obtained, continuously and separately adding feed of a constant monomeric ratio and catalyst to the equilibrium mixture, at such rates as to maintain a constant percent conversion to polymer, and rapidly agitating the mixture so that the reactants and catalyst are'diluted and mixed into the main polymerization mixture before little, if any, polymerizationoccurs. Simultaneo'usly, a suflicient volume of reactants plus polymer is removed continously from the reactor to maintain the reactor at constant volume. It is important that the conversion be maintained in the reactor at less than 100%, usually less than and preferably less than 90%. If the'reaction' at any time goes to completion, i. e. in thereactor, there would be no monomers in the overflow and hence none in the reactor, so that if polymerization'istaking place, it mustb occurrin'g'before the fee'd is'di'luted to equilibrium conditions. conversion is maintaine'dbelow 90 or 95% then the concentrati in of monomers and. polymer product-.111 the reactor area'u maintained constant by the"continlia1 equilibrium addition of eed and withdrawal of product, if agitation is Sunciently rapid. {Ithis' constancy of reactant concentration substantially eliminates compasses: a1 heterogeneity, reduces molecular weight net-er; ogeneity, and produces-aclear transparent prod- T;

It is to benoted that the monomer ratio in thefeed and that inthe reactor under equilibrium conditions will not be the same. The reactor liquid will be richer than the feed in the monomer On the other hand, if a constant with the slower copolymerization rate. The ratio required in the feed in order to produce a desired ratio in the polymer is readily determined experimentally, however, since it is constant at a constant conversion.

Thus, the controlling conditions necessary for the process of this invention are: (1) constant monomer ratio in the feed; (2) essentially constant conversion; (3) dilution of the feed in the reactor to essentially equilibrium conditions before much polymerization takes place, by the use of rapid agitation and less than complete conversion; (4) constant reactor volume; and

(5) continuous operation All types of continuous polymerization are not suitable for the above process. For example, a coil type reactor in which feed and catalyst are introduced into one end of a pipe and product withdrawn at the other end, is entirely unsuitable for the present process, because of the lack of end to end mixing and the consequential variation in polymerization conditions along the pipe.

The invention has been found particularly applicable to the copolymerization of isobutylene or other alkenes of 3-5 carbon atoms, and styrene or substituted styrenes having 1 to 2 substituent halogen atoms, e. g., chlorine, or lower alkyl, e. g. methyl, ethyl, etc., groups, by the general process described in U. S. Patent No. 2,274,749. In general, the process is carried out in the presence of an inert solvent or diluent such as liquefied propane or butane or a lower alkyl halide such as methyl or ethyl chloride. The catalyst comprises a Friedel-Crafts metal halide, such as boron fluoride or aluminum chloride, or other halide disclosed by N. O. Calloway in his article on the "Friedel-Crafts Synthesis appearing in Chemical Reviews, vol. 17, No. 3, page 375, preferably dissolved in a solvent which forms no complex with the halide and which is liquid at the reaction temperature such as ethyl or methyl chloride. The reaction temperature should be at least as low as 50 C. and may be as low as -103 C. or lower.

For best results, the feed monomer ratio should extend from 40% to 80% styrene by weight and the conversion from to 90%, preferably from to 85%.

The following examples illustrate the process of this invention:

Ewample 1 0 A feed consisting of parts styrene, 30 parts isobutylene, and 300 parts methyl chloride, by weight, was polymerized in an ethylene jacketed 3.1 liter agitated continuous overflow reactor with a catalyst consisting of 0.1 g. boron fluoride per 100 cc. methyl chloride. The feed rate, 71.3 g./min., and the catalyst rate, 20 g./min. were such that the reactor contents were turned over in about /2 hour. The polymerization temperature was -92 C. Methanol was added at the exit of the reactor, and the reactor solution was later stirred into a large volume of methanol. The precipitated polymer was hot milled at 310 F. for 15 minutes. After 3 /2 hours operation of the reactor, the polymer was being produced at a conversion level of 44 per cent and'contained about 63 per cent styrene (by refractive index). This polymer had an intrinsic viscosity of 1.4 and was clear and colorless when molded into 1 x 3 x A slabs, under pressure'at 300- F. for 2 min. and, while under pressure, cooled to room temperature. It also had a tensile strength of 3650'lbs./sq. in., and an elongation of 30%.

Example 2 A feed consisting of 60 parts styrene, 40 parts isobutylene, and 186 parts of methyl chloride was polymerized in an ethylene jacketed 3.1 liter con tinuous overflow agitated reactor with a catalyst consisting of 0.25'g. aluminum chloride per 100 cc. methyl chloride. The feed and catalyst rates were such that the reactor contents were turned over in about /2 hour. At the start of the reac tion, it is, of course, necessary to increase the conversion from zero to the desired per cent conversion, so that the polymerization is not taking place under equilibrium conditions. As time goes on, however, the polymer made during this period is worked out of the system, and the conditions of the invention are established, so that clear, transparent polymer is made. This is illustrated by the following data on polymer precipitated from the reactor liquor with methanol, hot milled 15 minutes at 310 F., and molded into thick slabs:

Percent Transmis- Polymer sion of Light Percent I t Period Made During Conl K Run Hour version Reading 1 Reading 2 l 40.0 40.0 23.3 1.32 A l to 1. 55.0 55. 5 37. 3 1.06 1.5 to 2.0 80. 5 80. O 40. 5 0. 96 2.0 to 2.5 84.0 85.0 43. 4 0.87 2.5 to 3.0 89. 0 88.0 42. 7 O. 89 3.0 to 3.5. 90.0 87. 0 41. 3 0. 86 B 3.5 to 4.0. 89. 0 89. 5 45.0 0.84 4.0 to 4.5. 49. 0 0. 82 4.5 to 5.0 r. 45. 8 0.85

Average. 44. 7 0. 85

A feed consisting of 65 parts styrene, 35 parts isobutylene and 186 parts methyl chloride was polymerized as described in Examples 1 and 2 with a catalyst consisting of 0.1 g. aluminum chloride per cc. methyl chloride. After 4.5 hours of operation, polymer was being produced at 81 per cent conversion, containing 59 per cent styrene, had. an intrinsic viscosity of 0.73, and transmitted 87.5 per cent of incident light through a /4 thick slab when tested as in Example 2.

Example 4 A feed consisting of 71.2 parts styrene, 28.3 parts isobutylene, and 550 parts methyl chloride was polymerized as in Examples 1 and 2 with 0.25 g. aluminum chloride per' 100 cc. methyl chloride as catalyst. At the end of 3.5 hours operation, polymer was being produced at 57 per cent conversion, contained 65.2 per cent styrene, and

transmitted 92 per cent of incident light through a A" specimen when measured as in Example 2.

Example 5 A feed consisting of 57.5 partsstyrene, 42.5

p'arts isobutylene, and 300 parts of methyl chloride -wa's polymeri'ze'd,- at -'-87-'-C., as in Examples "1 and -'2 with a A catalyst consisting -of 021 .aluminum-chlorideper100-cc methyl chloride. At the 'en'd of-4l25 hours operation, polymer having an intrinsic viscosity of 1.15 was being produced at 49 per cent conversion, contained 45 per cent styrene, and transmitted '76. per cent of incident light through a specimen when measured as in Example 2.

Examples 6, 7 and 8 These three experiments were made, in :gen-

-eral, like 'the copolymerizations of theprevious styrene by determinationof refractive index,-and i-tested forintrinsic viscosity. The results of ;-these fractionation-studies are tabulated herebelow,;.together'with corresponding :data on fractions obtained from 'the corresponding styrene-isobutylene copolymer made by :batch polymerization under substantially similar conditions (except *that the catalyst used was aluminumchloride instead of boron 5 fluoride) 7 Batch Continuous Fraction Percent Percent.

Percent Oom- I V Percent "Comv of Total bined oflotal bined Styrene Styrene Total wt. of fractions within =l=4.% of styrene:

B (batch), 11.8%/Wt. C (continuous), 76.2%Iwt.

These fractionation data show that the batch Percent Percent Feed, Run Percent Styrene Ex. Mono- Percent Length, Oonverin .25 11 mers Styrene Hours sion Polymer mission y 14 53. 2 4. 5 67 43. 7 65. 0 0. 97 20 47. 0 4. 5 63 36. 1 32. O 0. 96 2O 40. O 2. 5 39 20. 4 14. 5 1. 3

These data show that as the proportion of styrene in the feed is reduced (compared to that of isobutylene), the proportion of styrene entering the copolymer molecules becomes even still less, and it becomes increasingly more diflicult to produce a polymerization product having I a high per cent of light transmission.

Example 9 For comparison, two styrene-isobutylene copolymers were made each with a combined styrene content of about 60% by weight, but one being made by a batch operation, and the other by the continuous polymerization to partial conversion according to the present invention.

The continuous operation was carried out in the same general manner as the previous examples, by continuously feeding into a polymerization reactor a monomer feed consisting of 67.5% by weight of styrene and balance isobutylene, dissolved in 3 parts of methyl chloride per part of mixed monomers, maintaining this polymerization mixture at a temperature of about -92 C., the catalyst solution continuously fed into the polymerization mixture being 0.1% by weight of BF3 per 100 cc. of methyl chloride. This polymerization was carried out continuously until the conversion reached about 40% by weight under substantial equilibrium conditions. The copolymer being thus produced had a combined styrene content of 60% and an intrinsic viscosity of 1.38. In order to fractionate the total polymerization product, it was dissolved in 4% concentration in toluene, and then successive portions of polymer were precipitated by adding successive increments of methanol and recovering the polymer precipitated. Each of the fractions was weighed, analyzed for per cent combined polymerization product contained only about 12% by weight of constituents coming within the desired composition limits of :4=% of the average 60% combined styrene, whereas the continuous polymerization product, made according to the present invention, contained 76% by weight of constituents coming within this desired limit.

This shows that the present invention produces a substantially homogeneous product.

Also, the good light-transmitting properties of products made by the present invention may be contrasted with those obtained when the polymer is prepared by putting a batch of feed in a reactor and adding catalyst with agitation until essentially complete conversion is obtained. Exremely heterogeneous polymer is obtained under these conditions, since the concentrations and the ratio r of the monomers in the reactor varies widely as the conversion is increased. The following data were obtained on polymers prepared in this manner, the light transmission being obtained on A," thick slabs as in Example 2:

Overall Sty- Percent Sample mm Light Transof Polymer, mission Percent 7 Y chloride dissolved in methyl chloride as solvent, the improvement which comprises maintaining a continuously agitated polymerizing mixtur of said styrene and isobutylene in a constant concentration in 2 to 4 volumes of methyl chloride as solvent and at a constant volume, maintaining a substantially constant conversion level of said polymerizing mixture at about 40 to 80% conversion, continuously adding a mixture of 38 to 32% by Weight of isobutylene and 62 to 68% by Weight of styrene in a substantially fixed ratio relative to each other to said polymerizing mixture, simultaneously continuously removing isobutylene, styrene and a copolymerization product containing about 58 to 62% combined styrene and having an intrinsic viscosity of about 0.7 to 1.5 and a light transmission of at least 60% in 8 molded layer from the polymerizing mixture, and adjusting the ratio of the total amount of isobutylene and styrene added to the mixture of isobutylene, styrene andproduct removed so that the concentration of isobutylene and styrene and product in the polymerizing mixture is maintained constant. 7

ROBERT F. LEARY'.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,274,749 Smyers Mar. 3, 1942 2,420,330 Shriver May 13, 1947 2,482,771 Heerema Sept. 27, 1949 2,491,525 Sparks Dec. 20, 1949 

